Background/Aims: Osteogenesis Imperfecta (OI) is a bone disease characterized by bone fragility, deformities, and multiple fractures. The aim of this study was to compare the different methods of measuring the basal metabolic rate (BMR) and body composition (BC) in pediatric patients with OI. Methods: This cross-sectional study included 52 individuals with a median age of 9 (5.25–12.7) years. BMR was calculated by bioelectrical impedance analyses (BIA), predictive values according to age from the World Health Organization (WHO), a kcal/cm formula, and indirect calorimetry (IC). BC was assessed using the anthropometric calculation of percentage body fat (%BF) and lean mass (kg), BIA, and dual-energy X-ray absorptiometry (DEXA). Agreement among the methods was assessed using the Bland-Altman technique. Results: IC estimates of BMR were greater than BIA and lower than values obtained using the WHO and kcal/cm methods. Better agreement was observed using the WHO values for mild forms of OI and the kcal/cm formula for moderate-to-severe forms. For BC, DEXA estimates of %BF were higher and the lean mass was lower than the values obtained using BIA and anthropometry. Neither method agreed with the DEXA method results. Conclusions: Significant differences exist among the various methods used for measuring BMR and BC with regard to phenotypic differences between OI types.